There are many industrial applications utilizing one or more sized granular materials. One particularly noteworthy application is a foundry which performs the process of casting metals, e.g., by making sand castings. In casting processes, a mold is made by packing molding sand around a pattern.
Molding sand consists of silica grains held together by some bonding material such as clay or bentonite. Grain size greatly influences the surface finish of a casting with the proper grain size being determined by the size of the casting, the quality of surface required, and the surface tension of the molten metal. When maximum permeability is desired, the grain size should be approximately uniform.
For this purpose, it is important for the sand to be classified, i.e., to have a known, uniform grain size. This has typically been done by utilizing a material classifying apparatus involving one or more separator screens where the sand travels a considerable straight-line distance over the screen to complete the separation. If the sand does not traverse a given distance, it has been found that the separation is incomplete and the grain size of the sand is not uniform.
Because of this requirement, most material classifying apparatus have occupied considerable space. The mere length of the path of travel required to assure complete separation has required such devices to be very large in size which not only occupies an undo amount of plant space but also has involved considerable capital expenditures to purchase and maintain the necessary equipment. Moreover, with regard to attempts to overcome such problems, it is known that another factor must be properly considered Namely, if the sand is to proceed in other than a straight line, i.e., a longitudinal path, the separator screen or screens must be mounted under tension in a precise manner. It is essential that the screen or screens not be distorted in any manner which would disturb the mesh size thereof at any point in the path of travel to avoid non-uniform grain size in the sand that will be used in the casting process. In other words, it is known to be important to apply uniform tension to the separator screens.
While the discussion has focused on a foundry application, it will be appreciated that the same problems exist wherever a granular material must be of uniform grain size. This could encompass a wide variety of industrial applications, ranging from the foundry process described to, e.g., the confection industry. Accordingly, the problem in handling sand in a foundry is presented as merely representative.
The present invention is directed to overcoming the above stated problems and accomplishing the stated objects by providing a unique material classifying apparatus.